Evidence in Stratum for Shichahai Becaming Lake from Han-Dynasty to Yuan-Dynasty: A Case of the Southern Section at the Western Side of Building Site in Xiaoshibei Hutong
Based on the synthetically analysis to the data of the granularity, the chemical index and the sporopollen of the sectional sediments which belong to the building site located in Xiaoshibeihutong at the north bank of Shichahai, it shows the geomorphic changes of Shichahai from Han-Dynasty to Yuan-Dynasty. The changes can be divided into four parts according to the different periods. From 1930 to 1820 aBP, as the sediment of river form, it owns the branchchannel and sediment of fluvial facies. From 1820 to 1295 aBP, as the sediment of lake form lacustrine facies, especially from the end of Eastern-Han-Dynasty to Three-State-Period, it owns larger aquatorium and deeper water. During this time, the Chexiangqu was being built, thus it may have the man-made impoundment, but then it became lakeshore. From 1295 to 970 aBP, it is the sediment of fluvial facies. From 970 to 580 aBP, as the sediment of lakeshore, it would be the brim of north bank of Shichahai at that time. The series of sporopollen indicate not only the climate changes of this section, but also the characteristics of the vegetation in the carse relating to the local landform. It is found that the distance between the lakeshore in Yuan-Dynasty and Xie- Street in Yuan-Dynasty is about 100 meters, while the distance between the lakeshore in Yuan-Dynasty and the north bank of Shichahai is 80 meters. By analyzing the palaeoenvironment index of this section and the historical documents, the environmental envolution at Shichahai could be revealed, especially at this site, which provides the basic information for researching the environment changes of Shichahai.